1. Field of the Invention
The present invention generally relates to computer graphics. More particularly, the present invention relates to a method of selectively rendering graphic objects three-dimensional (3D) by relation map function.
2. Description of the Related Art
The growing popularity of computers has enabled conventional film clips, graphics and pictures to be digitized for computer processing, allowing special visual effects never before possible. Computer imaging or graphing is also gaining a foothold in almost every profession because of the widespread use of computers. However, the restricted features of the video display and the computer have made typical computer applications more suitable for processing 2-D graphic objects and for presenting 2-D effects rather than for processing 3-D graphic objects and presenting 3-D effects.
The conventional method for achieving 3-D effect uses the polygonal approach. In said polygonal approach, a 2-D planar graphics is first determined and segmented into a plurality of polygons with computer operations. Then an interpolation operation is performed to change the associated color value of the pixels of each polygon to render 3-D visual effects. Generally speaking, the 2-D original graphic is usually composed of smooth curves of polynomials and the smooth and gradual visual effect is usually desired. Whereas, the effect of conventional method using plural polygons to change the color values of the pixels is not so satisfactory. For example, if not enough polygons applied, the zigzag distortion will happen on the lines corresponding to the curves of the 2-D original graphic. Thus, the visual effect is adversely affected.
In another way, if the applied polygons are increased to avoid the above-mentioned problem, the processing time will be considerably increased. Additionally, if different kinds of visual effects are desired on a 2-D original graphic, every corresponding segmenting way may be accordingly different and the processing time can be also increased.
Another processing method of rendering 3-D graphic effects with a 2-D graphic object is disclosed in the U.S. Pat. No. 5,828,380 assigned to Ulead Systems, Inc. In said processing method, a relation mapping function is first given for each pixel of the graphic to obtain the directional relation of the corresponding 2-D graphic object. The required 3-D imaging effects, such as generating the measurement of length corresponding to the third axis (i.e., z-axis), can be generated from the acquired directional relation through an effect function to actualize 3-D visual effects.
FIG. 1 illustrates the relation map function corresponding to several pixels of a picture as specified in U.S. Pat. No. 5,828,380. As shown in FIG. 1, a 2-D graphic object is composed of a ring-shaped area confined by closed curves P0 and P1. The 2-D graphic object is composed of numerous pixels, such as A1, A2, and A3. In said processing method, a relation map function corresponding to pixels of the 2-D original graphics is first obtained, which represents a distance or a vector from every pixel to the corresponding edge of the closed curves P0 or P1 located closest thereto. In FIG. 1, the relation map function represents the directional relation of the vectors from every pixel to the edges located closest thereto, such as {overscore (xcexd)}1, {overscore (xcexd)}2, and {overscore (xcexd)}3.
Then, an effect function performs 3-D function of each vector {overscore (xcexd)} (corresponding to each pixel). In the effect function, a relation limit dmax is defined, denoting a range of pixels within the distance dmax from the edges of the 2-D graphic object. Only the pixels within dmax range need 3-D modeling processing such as effect on relation map (ERM) functions, whereas the pixels in each range determine the realistic 3-D effects being displayed according to a predetermined contour curve.
FIGS. 2a-2c illustrate three possible contour curves in accordance with the effect function. FIG. 2a is a type of rounded bevel, with C1 denoting a contour curve, and the coordinate of the pixel (x,y) starting from the edge within a relation limit dmax determines the corresponding coordinate on the axis z in accordance with said contour curve C1. Further, FIG. 2b is a type of straight bevel, with C2 denoting a contour curve; and FIG. 2c a combined type of two rounded bevels, with C3 denoting a contour curve.
Taking the rounded bevel type of FIG. 2a as an example, assume the distance from the coordinate of the pixel (x, y) to the edge of the corresponding edge is L(={square root over (x2+y2)}); then the z-axis parameters of said pixel (x,y) can be determined as follows:
z=Lxc3x97tan[cosxe2x88x921((dmaxxe2x88x92L)]xe2x80x83xe2x80x83(1)
The computations of z-axis parameters under other circumstances can also be made in a similar manner. In other words, the z-axis coordinate corresponding to each pixel within the relation limit dmax in the above contour curves can be calculated with mathematical equations.
Thus, the processing method of U.S. Pat. No. 5,828,380 can rapidly render a 3-D display with simple computations. However, the utilization of this method to selectively process 3-D graphic objects is burdensome.
Accordingly, it is an object of the present invention to provide a method to realize selective 3-D effects in a simpler manner.
The above object of this invention can be accomplished with a method of selectively rendering a 2-D graphic object having a plurality of closed curves three-dimensional. The closed curves are first defined as a unique outer closed curve and at least one inner closed curve, while the step of determining a mask in response to the closed curve follows. The mask is used to select a portion of the 2-D graphic object to be displayed in 3-D effects. Next, a directional relation is acquired in response to the outer closed curve and the mask. Then, z-axis parameters corresponding to pixels of the 2-D graphic object are generated in response to the directional relation. Therefore, a 3-D graphic object can be created in accordance with the 2-D graphic object and the z-axis parameters.